Non-volatile magnetic memory element with graded layer

ABSTRACT

A non-volatile magnetic memory element includes a number of layers one of which is a free layer which is graded. The graded free layer may include various elements with each element having a different anisotropy or it may include nonmagnetic compounds and magnetic regions with the non-magnetic compounds forming graded contents forming a unique shape such as cone shaped, diamond shaped or other shapes and whose thickness is based on the reactivity of the magnetic compound.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/253,918, filed on Oct. 5, 2011, by Rajiv Yadav Ranjan, andentitled “Non-Volatile Magnetic Memory Element with Graded Layer” andU.S. patent application Ser. No. 13/253,916, filed on Oct. 5, 2011, byRajiv Yadav Ranjan, and entitled “Non-Volatile Magnetic Memory Elementwith Graded Layer”, both of which claim priority to U.S. patentapplication Ser. No. 11/776,692, filed on Jul. 12, 2007, by Rajiv YadavRanjan, and entitled “Non-Volatile Magnetic Memory Element With GradedLayer”, which is a continuation-in-part of U.S. patent application Ser.No. 11/740,861, entitled “A High Capacity Low Cost Multi-Stacked CrossLine Magnetic Memory”, filed on Apr. 26, 2007, which is acontinuation-in-part of U.S. patent application Ser. No. 11/739,648entitled “Non-Volatile Magnetic Memory With Low Switching Current AndHigh Thermal Stability”, filed on Apr. 24, 2007, which is acontinuation-in-part of U.S. patent application Ser. No. 11/678,515entitled “A High Capacity Low Cost Multi-State Magnetic Memory”, filedon Feb. 23, 2007, which is a continuation-in-part of U.S. patentapplication Ser. No. 11/674,124 entitled “Non-uniform Switching BasedNon-Volatile Magnetic Base Memory”, filed on Feb. 12, 2007, thedisclosures of which are incorporated herein by reference, as though setforth in full.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to non-volatile magnetic memoryand particularly to non-volatile magnetic memory having graded layer(s).

2. Description of the Prior Art

Computers conventionally use rotating magnetic media, such as hard diskdrives (HDDs), for data storage. Though widely used and commonlyaccepted, such media suffer from a variety of deficiencies, such asaccess latency, higher power dissipation, large physical size andinability to withstand any physical shock. Thus, there is a need for anew type of storage device devoid of such drawbacks.

Other dominant storage devices are dynamic random access memory (DRAM)and static RAM (SRAM) which are volatile and very costly but have fastrandom read/write access time. Solid state storage, such assolid-state-nonvolatile-memory (SSNVM) devices having memory structuresmade of NOR/NAND-based Flash memory, providing fast access time,increased input/output (JO) speed, decreased power dissipation andphysical size and increased reliability but at a higher cost which tendsto be generally multiple times higher than hard disk drives (HDDs).

Although NAND-based flash memory is more costly than HDD's, it hasreplaced magnetic hard drives in many applications such as digitalcameras, MP3-players, cell phones, and hand held multimedia devices due,at least in part, to its characteristic of being able to retain dataeven when power is disconnected. However, as memory dimensionrequirements are dictating decreased sizes, scalability is becoming anissue because the designs of NAND-based Flash memory and DRAM memory arebecoming difficult to scale with smaller dimensions. For example,NAND-based flash memory has issues related to capacitive coupling, fewelectrons/bit, poor error-rate performance and reduced reliability dueto decreased read-write endurance. Read-write endurance refers to thenumber of reading, writing and erase cycles before the memory starts todegrade in performance due primarily to the high voltages required inthe program, erase cycles.

It is believed that NAND flash would be extremely difficult to scalebelow 45 nanometers (nm). Likewise, DRAM has issues related to scalingof the trench capacitors leading to very complex designs which arebecoming increasingly difficult to manufacture, leading to higher cost.

Currently, applications commonly employ combinations of EEPROM/NOR,NAND, HDD, and DRAM memory in a system design. Design of differentmemory technology in a product adds to design complexity, time to marketand increased costs. For example, in hand-held multi-media applicationsincorporating various memory technologies, such as NAND Flash, DRAM andEEPROM/NOR flash memory, complexity of design is increased as aremanufacturing costs and time to market. Another disadvantage is theincrease in size of a device that incorporates all of these types ofmemories therein.

There has been an extensive effort in development of alternativetechnologies, such as Ovanic random access memory (RAM) (or phase-changememory), Ferro-electric RAM (FeRAM), Magnetic RAM (MRAM), probe-storage,made by Nanochip, Inc. of Fremont, Calif., and others to replacememories used in current designs such as dynamic RAM (DRAM), static RAM(SRAM), electrically erasable and programmable read-only-memory(EEPROM)/NOR flash, NAND flash and hard disk drive (HDD) in one form oranother. Although these various memory/storage technologies have createdmany challenges, there have been advances made in this field in recentyears. MRAM seems to lead the way in terms of its progress in the pastfew years to replace all types of memories in the system as a universalmemory solution.

One of the problems with prior art memory structures including MRAMs istheir cell or memory size being too large therefore not lending itselfwell to scalability. A typical design of such MRAMs uses one or moretransistors for one memory cells that lead to nT-1mem cell type designwhere n=1-6. This makes the cell size too large leading to issues ofscalability and cost. Recently, current-induced magnetization switching(CIMS) is being explored as an alternative memory solution, andallegedly introduces a better way of building higher capacity MRAM typememory. But memories based on MRAM tend to have larger cell size(16-24F², where F is the minimum feature based on the lithographytechnology). There is also a tradeoff between low-switching-current, andreliability of the memory associated with thermal stability.

Therefore, in light of the foregoing, what is needed is a non-volatilemagnetic memory element, which has both low switching current whileexhibiting improved reliability.

SUMMARY OF THE INVENTION

To overcome the limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa method and a corresponding structure for a non-volatile magneticstorage memory device that is based oncurrent-induced-magnetization-switching having reduced switching currentin the magnetic memory and high memory capacity.

Briefly, an embodiment of the present invention includes a non-volatilemagnetic memory element formed of a fixed layer on top of which isformed a tunnel layer on top of which is formed a graded free layer.

These and other objects and advantages of the present invention will nodoubt become apparent to those skilled in the art after having read thefollowing detailed description of the preferred embodiments illustratedin the several figures of the drawing.

IN THE DRAWINGS

FIG. 1 shows relevant layers of a non-volatile magnetic memory element10, in accordance with an embodiment of the present invention.

FIG. 2 shows further details of the layers of the memory element 10 ofFIG. 1.

FIG. 2( a) shows a non-volatile magnetic memory element 11, inaccordance with an alternative embodiment of the present invention.

FIG. 3 shows states of the layer 26 as the memory element 10 isprogrammed.

FIG. 4 shows certain portions of an exemplary embodiment of the memoryelement 10.

FIG. 5 shows a graphical representation of the amount of reactive gasapplied as a function of time during deposition of any of the gradedlayers.

FIG. 6 shows certain portions of the memory element 10 in accordancewith another embodiment of the present invention.

FIG. 7 shows a graphical representation of the percentage of reactivegas, shown by the x-axis, applied during deposition of the layer 26 vs.the deposition time, shown in the x-axis, of any of the graded layers.

FIG. 8 (a) shows certain layers of the memory element 10 in accordancewith yet another embodiment of the preset invention.

FIG. 8 (b) shows certain layers of the memory element 10 in accordancewith yet another embodiment of the preset invention.

FIG. 8 (c) shows the composition profile in the graded layers inaccordance with yet another embodiment of the preset invention.

FIG. 9 shows a magnetic tunnel junction, such as in the memory element10 with an access transistor, in accordance with an embodiment of thepresent invention.

FIG. 10 shows a sensing circuit 210 including the memory element 100 forsensing or measuring the state of (reading) the memory element 100, inaccordance with an embodiment of the present invention.

FIG. 11 shows a non-volatile memory integrated circuit 300 showing anapplication of the memory element 10 of the foregoing embodiments.

FIG. 12 shows a process flow chart 310 showing the steps performed inmanufacturing the memory element 10 and corresponding CMOS circuitry.

FIG. 13 shows the graded free layer 26 having out-of-plane magneticanisotropy, in accordance with another embodiment of the presentinvention.

FIG. 14 shows a non-volatile magnetic memory element 519, in accordancewith another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the embodiments, reference is made tothe accompanying drawings that form a part hereof, and in which is shownby way of illustration of the specific embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized because structural changes may be madewithout departing from the scope of the present invention. It should benoted that the figures discussed herein are not drawn to scale andthicknesses of lines are not indicative of actual sizes.

In an embodiment of the present invention, a non-volatile magneticmemory element is disclosed. In one embodiment of the present invention,the memory element includes a graded fixed layer, a tunnel layer and agraded free layer, the fixed layer, tunneling layer and free layercomprising a magnetic tunnel junction (MTJ). The memory element isstackable into arrays of memory elements.

Referring now to FIG. 1, relevant layers of a non-volatile magneticmemory element 10 is shown, in accordance with an embodiment of thepresent invention. The memory element 10 is shown to include a fixedlayer 12 on top of which is shown formed a tunnel layer 14 on top ofwhich is shown formed a graded free layer 16. It should be noted thatthe drawings and figures shown herein are not drawn to scale. It shouldbe noted that while throughout the following discussion andillustrations, the layer 16 or other free layers will be discussed asgraded, the layer 12 may also be graded, in an alternative embodiment.Still alternatively, both layers 16 and 12 may be graded layers.

FIG. 2 shows further details of the layers of the memory element 10 ofFIG. 1. In FIG. 2, an anti-ferromagnetic pinning layer 20 formed on topof a seeding (or seed) layer 19, which is shown formed on top of abottom electrode 18 on top of which is shown formed a fixed layer 22 ontop of which is shown formed a tunnel layer 24 on top of which is shownformed a graded free layer 26 on top of which is shown formed a caplayer 28 on top of which is shown formed a top electrode 30. The fixedlayer 22 is similar to the layer 12 and the tunnel layer, which issynonymously referred to as a barrier layer, is similar to the tunnellayer 14 and the free layer 26 is similar to the free layer 16. Thefixed layer 22 is shown to include a sub fixed layer 32 on top of whichis shown formed a synthetic anti-ferromagnetic (AF) coupling layer 34 ontop of which is formed a sub fixed layer 36.

During deposition of the free layer 26, the deposition process is variedduring the deposition of the layer causing grading of the free layer 26,as will be shortly further discussed. Alternatively, the layer 22 may bea graded layer, in which case it is built in a manner similar to that ofbuilding or forming the layer 26, as further discussed below. A gradedlayer, such as the layer 26, is formed during the deposition process byvarying the amount of oxygen or other reactive gas components in thesputtering gas, by varying the total sputtering gas pressure, by varyingthe substrate bias applied to the wafer, by varying the sputtering powerapplied to the target, by varying the ratio of sputtering powers to twoor more targets during co-deposition, by bombarding the growing filmwith ions from a separate ion source or a combination of one or more ofthe foregoing. An exemplary sputtering gas is Argon, another example isxenon (Xe), krypton (Kr) or any other type of inert gases.

In an exemplary deposition method, gas pressure is varied monotonically,i.e. increasingly, from 0.5 to 10 milliTorr (mTorr) during deposition ofthe graded layer(s) which results in a gradual changing of thecomposition of the graded layer(s) as well as microstructure change.Monotonically refers to changing the gas pressure in an increasingdirection over time.

In a yet another example, the target power density during sputtering isvaried in a monotonic (increasing) manner from 0.1 to 1.0 Watts percentimeter squared (W/cm2) during the deposition of the graded layers toaccount for various target sizes. Target (or cathode) is the source ofthe material that is sputtered (or any other type of physical orchemical wafer deposition) onto the wafer or substrate.

In yet another case, two different targets are employed and the gradedlayer is made by co-deposition from the two different targets, the powerdensity in one target is caused to be ramped up monotonically from 0.1W/cm2 to 1 W/cm2 while the power density of the other target is rampeddown from 1 W/cm2 to 0.1 W/cm2 which results in a gradually-changingcomposition through the film thickness of the graded layer.

In the foregoing examples using targets, alternatively, a negativevoltage is applied to the wafer to enhance the bombardment of sputteringgas during deposition resulting in a changing composition andmicrostructure of the graded layer. Typical voltages range from −50 to−100 Volts. Substrate or wafer includes a number of memory cells.Alternatively, a radio frequency (RF)-based voltage may be employed.

In still another example, a separate ion source is employed to enhancethe bombardment of sputtering gas during deposition resulting in achanging composition and microstructure of the graded layer. While thisadvantageously allows changing the ion source location and thereby theenergy of the bombarded ions, it is more costly.

In one embodiment of the present invention, the tunnel layer 24 is madeof titanium dioxide (TiO₂), alumina (Al₂O₃), magnesium oxide (MgO),tantalum oxide (Ta₂O₅), hafnium oxide (HfO₂), zirconium oxide (ZrO₂),tantalum nitride (TaN), strontium oxide (SrO), ruthenium oxide (RuO), orzinc oxide (ZnO). MgO, containing less than 50 mol % of the compoundsfrom the foregoing list of components, is well suited to form the tunnellayer 24.

The layer 28 serves to insulate the layer 26 from the top electrode 30and in this manner, serves to isolate the layer 26 from anymicro-structural effects of the top electrode 30. The choice of materialfrom which the top electrode 30 is made depends, at least in part, onthe choice and availability of the etching process which is employed todefine the size of the memory element 10. There are a number of choicesof etching processes, such as, reactive etching process and ion-beametching process. Reactive etching process is better suited forproduction and may employ different gases depending on the material fromwhich the top electrode 30 is made.

In one embodiment of the present invention, the cap layer 28 is made ofmaterial selected from a group of amorphous materials such as nickelniobium (NiNb), nickel zirconium (NiZr), nickel niobium zirconium(NiNbZr), nickel silicon niobium (NiSiNb), or nickel silicon zirconium(NiSiZr). In yet another embodiment of the present invention, the caplayer comprises more than one layer including another layer chosen fromtantalum (Ta), tantalum nitride (TaN), titanium (Ti), titanium nitride(TiN), copper (Cu), gold (Au) and ruthenium (Ru). A typical thickness ofthe layer 28 is less than 50 nm.

In one embodiment of the present invention, the bottom electrode 18 ismade of a non-magnetic layer, such as, for example, tantalum (Ta) andusing reactive ion etching (RIE) process. The seeding layer 19 which isformed on top of the layer 18 has the purpose to promote properpolycrystalline growth of the layer 20, has large enough conductivityand at the same time acts as a smoothening layer to ensure low surfaceroughness for the subsequent layers (formed thereatop) leading to a lowsurface roughness of the layer 24. Exemplary material forming theseeding layer 19 are Ta, Ru—X or NiFeY, where X and Y include one ormore of the elements from the following group: chromium (Cr), molybdenum(Mo), tantalum (Ta), tungsten (W), zirconium (Zr), rhodium (Rh) oriridium (Ir). The seeding layer 19 serves to achieve proper crystallineorientation of the layer 20. The layer 20 is an AF magnetic layer thatessentially determines the direction of magnetization of the layer 22.

In one embodiment of the present invention, the layer 34 is made of analloy made of ruthenium (Ru) and element X which may include one or moreof the elements from the following group: chromium (Cr), molybdenum(Mo), tantalum (Ta), rhodium (Rh) or iridium (Ir) which creates RKKYcoupling between the adjacent magnetic layers namely, the layers 32 and36. The choice of thickness of the layer 34 results in a parallel oranti-parallel magnetization across the magnetic layers 32 and 36. Forexample, typically a thickness of 6 Å to 10 Å results in a stronganti-parallel coupling between the two adjacent magnetic layers while athickness of 12 Å to 18 Å results in parallel coupling.

The choice of alloy for layers 32 and 36 is one or many ferromagneticelements, such as Co, Fe and Ni, and contains less than 20 atomicpercent of platinum (Pt) and further contains up to 20 atomic percent ofone or more of the following elements: P, B, Cr, Ta, W, Mo, Zr, Hf. Thelayer 36 is a substantially amorphous alloy, such as a CoFeCrB, wherethe boron, B, content of the alloy is typically in the range of 10 to 30atomic percent which makes the as-sputtered layer amorphous. In asubsequent heating process, the layer 36 in conjunction with the layer26, which is also amorphous in its as-deposited state, transform into acubic crystal structure having (002) plane that is substantiallyparallel to the layer 24, which has a cubic crystalline structure being(001), and having their crystal planes, (001), matched. In the FIG. 2,the layer 24 is substantially parallel to the horizontal lines and in adirection going into the plane of FIG. 2. Following the annealingprocess, the atomic planes of the layers 26 and 36 transform intocrystalline phase with their (002) crystal planes being horizontal andgoing into the plane of the FIG. 2. This type of structure results inthe memory element 10 having a very high TMR (tunnelingmagneto-resistance).

Gases are introduced during the deposition of the layer 26, and in anexemplary embodiment and manufacturing method of the present invention,such gases are made of argon (Ar—X), xenon (Xe—X) or krypton (Kr—X),where X is typically less than 50 vol % of one or more of the followingmaterial: oxygen gas (O₂), water (H₂O), nitrous oxide (NO₂), nitricoxide (NO), sulfur dioxide (SO₂), carbon monoxide (CO), carbon dioxide(CO₂), or phosphine (PH₃), phosphorous pentaoxide (P₂O₅). Examples ofthe increase in the percentage of these gases during the processing timeof deposition of layer 26 are shown in FIG. 7. In one embodiment, thepercentage of reactive gas in the sputtering (or carrier) gas is lessthan 20 vol % of the total gas with the remainder of the reactive gasmaking up the rest of the total gas. Examples of the material comprisingthe less than 20 vol % include H₂O, CO₂, CO, NO or NO₂. Examples ofmaterial comprising the remainder of the total gas include argon, xenonor krypton.

In an exemplary embodiment, the layers 32 and 36 are compounds of Co, Feand may contain nickel (Ni) as well as one or many elements from thefollowing list of elements: boron (B), phosphorous (P), chromium (Cr),tantalum (Ta), zirconium (Zr), silicon (Si), molybdenum (Mo), hafnium(Hf), or tungsten (W). In one embodiment of the present invention, thelayer 20 is made of iridium manganese (IrMn), platinum manganese (PtMn)or nickel manganese (NiMn) containing one or more of the elements fromthe list: chromium (Cr), nickel (Ni), or molybdenum (Mo).

In an exemplary embodiment, the layer 26 is made of ferromagneticmaterial and the layer 28 is made of non-magnetic material and the topelectrode 30 is made of non-magnetic material. An example of theferromagnetic material used to make the layer 26 is (CoFe)1-xBx where xis atomic fraction of B within the alloy composition and is typicallyless than 0.4. In an exemplary embodiment, the layer 36 is ferromagneticin characteristic as is the layer 32 and the layer 32 is made of theferromagnetic material (CoFe)1-yBy where y is atomic fraction of Bwithin the alloy composition and is typically is less than 0.4 and thelayer 36 is made of the ferromagnetic material (CoFe)1-xBx.

The bottom layer 18 which is formed below the layer 20 has multiplepurposes based on the process sequence. The bottom layer 18 acts as thebottom electrode for the magnetic memory and typically consists of morethan one layer. This layer need have large enough conductivity and atthe same time acts as a smoothening layer to ensure low surfaceroughness for the subsequent layers leading to a low roughness of thelayer 24. This is required in order to obtain a hightunneling-magneto-resistance (TMR) ratio. In one embodiment, the bottomlayer 18 comprises of multiple bi-layers of aluminum (Al) and copper(Cu) each having a thickness of less than 20 nm. In a yet anotherembodiment, a tantalum (Ta) layer is included having a thickness of lessthan 50 nm.

Typical thicknesses of the various layers shown in FIG. 2 are asfollows: the bottom layer 18 is less than 100 nanometers (nm), theseeding layer 19 is less than 20 nm, the layer 20 is less than 20 nm,the layer 32 is less than 10 nm, the layer 34 is less than 3 nm, layer36 is less than 10 nm, the layer 24 is less than 3 nm, the layer 26 isless than 20 nm, the layer 28 is less than 50 nm and the top electrode30 is less than 100 nm. In one embodiment of the present invention, thebottom electrode 18 is 50 nm, the layer 20 is 9 nm, the layer 32 is 4nm, the layer 34 is 1.2 nm, the layer 36 is 3 nm, the layer 24 is 1.2nm, the layer 26 is 4 nm, the layer 28 is 10 nm and the top electrode 30is 40 nm, in size.

In operation, current is applied to the element 10 in a direction, forexample, parallel to the page and from the bottom electrode 18 to thetop electrode 30. A current switching effect arises from the interactionbetween magnetic moments and the transport current. At least twodominant mechanisms are employed, namely, current induced magnetic fieldand spin-torque from the current induced spin polarization. In addition,there is also an effect from spin-accumulation at the interface of layer26 due to the discontinuous Fermi-level, which could also assist in theswitching of the layer 26 when appropriate current is applied such as aswitching current of less than 500 micro-amps for an elongated memoryelement having a dimension of less than 100 nm-by-200 nm and having anaspect ratio (=long axis/short axis) of between 1.2 to 3.

While the current-induced effect through the magnetic field is directlyproportional to the radius r, the latter spin-torque effect isproportional to r², where r is the distance from the current carryingelectrode to the layer 26. Torque is generated by spins through themomentum transfer of tunneled spin-polarized conduction electrons fromthe layer 22, which opposes the “intrinsic” damping of spins of thelayer 26. At sufficient current, such as between 200 micro amps (μA) to300 μA for a memory element of dimension between 100 nm-by-200 nm to 80nm-by-160 nm having a relatively oval shape along the y-axis. This canreverse the direction of the magnetization in the layer 26. A roughestimate of the critical current required for such switching isgenerally calculated in accordance with the following equation:

Ic=Ic _(0[)1−(k _(B) T/K _(u) V)ln(t _(p) /t ₀)]  Eq. (1)

Where Ic₀ is the critical switching current density without thermalfluctuation; k_(B) is the Boltzmann constant; T is the temperature;K_(u) is the effective uniaxial anisotropy and V is the volume of thefree-layer; t₀ is the inverse of the procession frequency of the spin(less than 1 ns); t_(p) is the pulse width of the switching current.

One way to reduce the critical switching is by reducing either K_(u) orV of the free layer 26. Additionally, the switching current can bereduced by lowering the thickness of the free layer 26, which may,however, compromise the reliability of the memory element 10 by makingthe size thereof more thermally unstable. Generally, a memory elementwith the free layer having higher K_(u) V is more thermally stable athigher temperatures. As a general rule, the magnetic energy, K_(u) V, ofthe free layer be greater than approximately 60 k_(B)T where, k_(B) isthe Boltzmann constant and T is the ambient temperature.

The embodiments of the present invention relies on the physics that themagnetization reversal takes place in a nano-seconds time scale, and onthe relative strengths of inter-granular exchange coupling andmagneto-static coupling between the neighboring grains. The exchangecoupling is generally much stronger than the magneto-static coupling.This could lead to different values of “V” corresponding to theswitching volume and the volume responsible for keeping the thermalstability. More specifically, in the embodiments of the presentinvention, the switching volume remains small while keeping the “volume”responsible for thermal stability large. This advantageously results ina lower “writing” or “programming” current while maintaining higherthermal stability.

One of the steps for manufacturing the memory element 10 is the magneticannealing process where the magnetic films are exposed to a magneticfield of 4-10 kOe applied in-plane of the wafer surface at a temperatureof typically over 350 C. In one embodiment, a magnetic field of 5 kOe isapplied parallel along the long, or easy, axis (for example an axis thatis parallel to the 150 nm axis for a 100 nm-by-150 nm memory cell) ofthe memory element 10 and parallel to the wafer surface at a temperatureof 375 degrees Celsius (C) for 2 hours. The role of the application ofthe magnetic field is to set the magnetic-orientation of the layer 20.At the same time, temperature annealing causes crystallization in theadjacent layers of layer 24, such as the layer 26 and the layer 36. Thishelps in ensuring high tunneling magneto-resistance (TMR), which isrelated to the ratio of resistance of two states which has a directimpact on the read-speed of the final memory. The foregoing descriptionof the operation/manufacturing process is intended to describe anexemplary embodiment thereof, thus, other ways of achieving the sameresults are anticipated.

In FIG. 2, the fixed layer 22 is shown to include a sub fixed layer 32on top of which is shown formed a synthetic anti-ferromagnetic (AF)coupling layer 34 on top of which is formed a sub fixed layer 36. In analternative embodiment, the layer 22 of FIG. 2 is graded, in the samemanner as described relative to the layer 26. In such an embodiment,only the sub fixed layers, such as the layers 36 and 32 of FIG. 2 aregraded.

In yet another embodiment of the present invention, both the free layer26 and the fixed layer 22 are graded, having changing compositionthrough the film thickness to ensure enhanced crystallization of thefree and fixed layers for high TMR as well as low switching current. Insuch an embodiment, the boron, B, content of the CoFeB alloy is variedthrough the film thickness of both the graded fixed and free layers insuch a manner that the composition of the fixed and free layer adjacentto the barrier layer is closer to 10 atomic percent and increases tomore than 20 atomic percent at the other interface of both the fixed andfree layers. In a yet another example, the fixed layer and thefree-layer have the composition of CoFeZrPtB where the B content isvaried in a similar manner for both the free and the fixed layers. Themechanism for such graded approach is that the atomic layers closer tothe barrier layer tend to crystallize at lower temperature first andthereby initiate the crystallization for the rest of the atomic layers.In the preferred modes, there is a gradual variation of boron whichcreates a gradual driving force for crystallization from the barrierlayer to the rest of the film. This results in a better transformationof the amorphous layers resulting in more coherent tunneling channelsand thereby leading to higher TMR. It is expected that such structurewill also have lower switching current characteristic.

FIG. 2( a) shows a non-volatile magnetic memory element 11, inaccordance with an alternative embodiment of the present invention. Thememory element 11 is shown to include the same layers as that of theembodiment of FIG. 2 except that some of the layers are formed indifferent orders. In FIG. 2( a), the memory element 11 is shown toinclude the bottom electrode 18 on top of which is shown formed aseeding layer 19 on top of which is formed the graded free layer 26. Ontop of the layer 26 is shown formed the barrier layer 24 on top of whichis shown formed the fixed layer 22 on top of which is shown formed thepinning layer 20. On top of the layer 20 is shown formed the cap layer28 and on top of the cap layer 28 is shown formed the top electrode. Thelayer 22 is formed of multiple layers, as shown and described relativeto FIG. 2. In FIG. 2( a), the sub fixed layer 36 is formed on top of thelayer 24 and the layer 20 is shown formed on top of the layer 32.

In alternative embodiments, any of the layers of the memory element 10are graded. Still alternatively, any combination of the layers of thememory element 10 are graded.

FIG. 3 shows states of the layer 26 as the memory element 10 isprogrammed. In FIG. 3, the physical alterations of the layer 26 lead tothe switching from one state to another of the memory element 10 andtherefore programmability or erasure thereof.

In FIG. 3, the layer 26 is shown to include two areas 44 and 42 whereenhanced switching of magnetic moment starts and builds up as a resultof the graded characteristic of the layer 26 thereby resulting in lowerswitching current density. A “graded” layer is a layer whose materialcharacteristics exhibit different properties such as the magnitude andthe direction of magnetic anisotropy vector thereof, composition ormicrostructure. Other examples of properties include magnetic moments,electrical conductivity, magneto-striction, or other magnetic orelectrical properties.

As the conduction electron carrying parallelizing spin enters from thebottom, i.e. the bottom electrode 18 for parallelizing process orreflected anti-parallel for anti-parallelizing process, the layer 26 isgraded, that is, non-uniform switching of the layer 26 is initiated andbuilds up to ultimately switch the state of the memory element 10, from,for example, parallel to anti-parallel to visa versa. Such build up isshown at 46 and the switching occurs with the direction of the state inthe direction shown by the arrows 48 of FIG. 3.

The embodiments of FIGS. 1-3 show a current-switching non-volatile MRAMwhich requires lower switching current and is scaleable to lowerlithographic dimensions. The free layer thereof includes oxides,nitrides, sulphides or phosphides based on the selection of gasintroduced during manufacturing. The content of the foregoing issubstantially nonmagnetic compounds varying across the thickness of thefree layer 26, which results in a film having “graded” contents of theoxides or the nitrides or the like. These films accentuate thenon-uniform switching process during the current-induced switching ofthe memory element 10 thereby leading to a low programming or erasecurrents.

FIG. 4 shows certain portions of an exemplary embodiment of the memoryelement 10. In FIG. 4, the layer 22 is shown on top of which is shownformed the tunnel (or barrier) layer 24 on top of which is shown thelayer 26. The layer 26 is shown to include a region 48 having asubstantially larger content of the aforementioned non-magneticcompounds, shown to be formed in the shape of an upside down conealthough other shapes are anticipated such as, but not limited to, theshapes shown at 50 and 52. The regions 49 are generally non-conductiveand may be either completely non-magnetic or partly magnetic dependingon the base alloy employed.

The more reactive the compound, the thicker the size of the region 49across. The thickness of each of the region 49 is determined by thefollowing equation:

Power×time α size of region 49  Eq. (2)

The length, in the vertical direction, of each of the region 49 is afunction of time. That is, the duration of time during which oxidization(nitridation or the like) occurs determines the vertical length of theregion 49. The regions 49 are made of oxides, nitrides or other materialpreviously noted. Since nitrous oxide (NO₂) is not as reactive as CO orO₂, it is advantageously used to form the compound in 49 from a processor manufacturing perspective. The regions 49 are essentially eachincreasing the amount of oxide formed from increasing amounts of thereactive gases.

In FIG. 4, magnetic regions (not including the region 49) 53 make up theremainder of the layer 26. Momentum transfer builds up to a criticalsize until an avalanche reversal occurs, switching the state of thememory element 10. In the embodiments of FIGS. 1-4, spin polarizedelectrons would not be conducted through their areas and will beconcentrated in substantially magnetic regions, thereby initiating“localized” switching leading to an avalanche type of switching. Forexample, if the base alloy used is CoFe and an oxidizing gas is usedsuch as H₂O, NO₂, then the regions 49 are comprised of mostly oxidizedcompounds of Co and Fe, such as CoO, Co₂O₃, FeO, Fe₂O₃ being in amixture. If the base alloy includes Cr, Ta, Mo, W or Ti, then the oxidesare of the types such as Cr₂O₃, CrO, Ta₂O₅, TaO, MoO, Mo₂O₃, W₂O₃, Wo,TiO₂ or TiOx.

FIG. 5 shows a graphical representation of the amount of reactive gasapplied as a function of time during deposition of any of the gradedlayers. FIG. 5 shows a graphical representation of the amount ofreactive gas content in the carrier gas, such as argon (Ar), appliedduring deposition of the free layer 26. The y-axis shows the percentageof the reactive in gas and the x-axis shows time.

FIG. 6 shows certain portions of the memory element 10 in accordancewith another embodiment of the present invention. In FIG. 6, the layer26 is shown to include oxides 54 made of, for example, Co and Fe. Theoxides 54 are generally non-magnetic or magnetic oxides. While the shapeof the oxides 54 appear as diamonds, other shaped-oxides may be formed,such as, but not limited to, oval or curved diamond. The diamond-shapedoxides 54 versus the oxides 53, are known to lower the switching andprogramming current of the memory element 10 due to their shape.Magnetic regions 56 make up the remainder of the layer 26.

FIG. 7 shows a graphical representation of the percentage of reactivegas, shown by the x-axis, applied during deposition of the layer 26 vs.the deposition time, shown in the x-axis, of any of the graded layers.In one embodiment, the reactive gas is Ar-5% NO₂ is premixed with theprimary gas Ar. The second gas Ar-5% NO₂ is introduced after 1 second ofstarting the deposition of layer 26 and is increased to 20% of the totalgas at 5 seconds from start and is dropped to zero after 9 seconds whilethe total deposition time of layer 26 is 10 seconds.

FIG. 8( a) shows certain layers of the memory element 10 in accordancewith yet another embodiment of the preset invention. In FIG. 8( a), thetunnel layer 24 is shown formed on top of the fixed layer 22 and on topof the tunnel layer 24 is shown formed the graded free layer 26, as inprevious embodiments. However, the layer 26 includes multiple elements60 rather than the single element, such as CoFeB, of previousembodiments. The multiple elements 60 are shown to include the elements62-68 although other number of elements may be employed.

The elements 60, in an exemplary embodiment, are made of (CoFe)1-xBxwherein x, in the case where the elements are non-magnetic, is chromium(Cr), tantalaum (Ta), tungsten (W), titanium (Ti), zirconium (Zr) orhafnium (Hf), which tend to oxide fast, whereas in the case where theelements are magnetic, x is typically less than 20 atomic percent. Mostof the momentum transfer starts at the element 62 and in the embodimentsof the present invention, the build up of and effective use of momenttransfer lowers current.

The element 62 generally exhibits a characteristic that is high in Ku oranisotropy, high in Co, for example, Co (70%) and Fe (30%), whereas theelement 64 exhibits mid Ku and the element 66 exhibits low Ku, forexample Co (30%) and Fe (70%).

In a yet another embodiment the Co/Fe ratio is changed from 0.8 to 1.2with 1 being Co(50 at %)Fe(50 at %). The composition gradient can bemade through a number of processing approaches. For example, it can bemade through using a multiple target system where each element has itsown power control which is varied separately to mix in the plasma. In ayet another approach, the gas flow, target power or the bias duringsputtering is varied to make different composition of the film throughthe thickness. A yet another approach may involve using a separateion-gun to generate elemental ions which are impinged on the growingfilm of layer 26 or layer 22 or both.

FIG. 8( b) shows yet another embodiment where the layers 22 and 26 areboth graded in such a manner that the composition of boron, B, is variedthrough the thickness. An example of percent boron through the film isshown in FIG. 8( c) where higher boron content is shown adjacent to thelayer 24 and the percent of boron drops away from the layer 24. In oneembodiment, the percent of boron is 20 atomic percent adjacent to thelayer 24 and drops down to 10 atomic percent at the edge of layers 22and 26.

FIG. 9 shows a magnetic tunnel junction (MTJ), such as the memoryelement 10 with an access transistor, in accordance with an embodimentof the present invention, forming a memory cell 90. In FIG. 9, thememory element 10 is shown coupled, through an electrode 92, to a bitline 96, on one of its ends, which is typically the top electrode 30. Onthe other end, the memory element 10 is shown connected, through abottom electrode (BE) 94 (such as the bottom electrode 18 of FIG. 2),through a contact, which is also shown coupled to a drain of atransistor 98. The transistor 98 further includes a source shown coupledto the program/erase line 204. The gate 200 of the transistor 94 isshown coupled to a word line 202. The electrode 92 is made of conductivematerial.

The embodiment of the FIG. 9 may be referred to as a single or 1-cellarchitecture. The MTJ (magnetic tunnel junction also referred to as thememory element 10) acts as the non-volatile memory element. The MTJelement has low resistance in the programmed state and higher resistancein the erased state. For example, in one embodiment of the presentinvention, the resistance for the low state is at least half of that ofthe high state. Low and high refer to binary states of ‘1’ and ‘0’ orvice versa. MTJ element or the memory element 100 is shown to have onetransistor in series with it for accessing the memory element. The bitline 96 is made of metal and the word line 202 is made of poly-silicon.

In operation, the memory element 10 is accessed in the following manner.The memory (or MTJ) element 10 in conjunction with the access transistor98 forms a memory cell 90. To program the memory cell 90, the bit line96 is connected to a positive power supply while the Program/Erase line204 is connected to ground. By accessing the memory cell 90, the wordline 202 is raised to a predetermined voltage, which turns thetransistor 98 ‘on’ and current flows from the bit line 96 to theProgram/Erase line 204. Electrons flow in the opposite direction andtravel through the fixed layer of the memory element 10 before enteringthe free layer. This causes the magnetic orientation of the free layerto align with the fix layer and the resistance (R) of the memory element10 to be dropped to a minimum. The erase operation, on the other hand,is performed by changing the direction of the bit line and theprogram/erase line. This time the Program/Erase line is biased positivewhile the bit line is grounded. The current will flow from Program/Eraseline to bit line, or electrons flow from bit line to Program/Erase line.Since the free and fix layers are magnetically aligned (programmedstate), then minority electrons are reflected from the fix layer backinto the free layer. These electrons have a spin orientation which isthe opposite of the fix layer. When they are injected into the freelayer, they apply a moment on the magnetic elements of the free layer inthe opposite direction. By pushing enough electrons through eventuallythe magnetic orientation of the free layers change in the anti-paralleldirection, and the MTJ resistance maximizes.

FIG. 10 shows a sensing circuit 210 including the memory element 100 forsensing or measuring the state of (reading) the memory element 100, inaccordance with an embodiment of the present invention. In FIG. 10, thesensing circuit 210 is shown to include a sense amplifier circuit 212coupled to a first decoding transistor 214 and further coupled to asecond decoding transistor 216, at their source. The drain of thetransistor 214 is shown coupled to a reference memory element (MTJ) 218and serves as a reference bit line. MTJs are each made of the memory100, in one embodiment of the present invention. The reference memoryelement 218 is further shown coupled to a transistor 242 at the drain ofthe transistor 242. The gate of the transistor 242 forms a referenceword line 220 and the source of the transistor 242 forms the Ver (orerase voltage) 238, which is shown coupled to the source of thetransistor 222.

The drain of the transistor 222 is shown coupled to the memory element100 and an opposite end of the memory element 100 is shown coupled tothe drain of the transistor 216 and forms the bit line 1 244. The erasevoltage 238 is similarly shown coupled to the source of the transistor224 and the gate of the transistor 224 is shown to form the word line 2228. The drain of the transistor 224 is shown coupled to the memoryelement 240, which on an opposite end thereto, forms the bit line 2 246.

The read operation will now be explained with reference to FIG. 10.During a read operation, the sense amplifier circuit 210 compares theresistance of the memory element 100 of the selected cell to theresistance of the reference memory element 218. The resistance of thecell 218 is designed to be (R1+R2)/2, where R1 is the resistance of thememory element 100 in a low state and R2 is the resistance of the memoryelement 100 in high state. The high and low states are based on thedescription provided above where the low state has a characteristic ofbeing at least half of the resistance of that of the high state. Themagnetic orientation of the fixed and the free layers are parallelrelative to each other at a low state and at a high state, the magneticorientation of the fixed and free layers are anti-parallel relative toeach other.

In one embodiment of the present invention, the sense amplifier 230 is abi-stable latch or any such device, which flips between states based onthe state of the resistance. For example, if resistance is low, thestate will be that of a low state and if resistance is high, the statewill be that of a high state.

It should be noted that the magnetic memory elements 100 and 240 are twoof many magnetic memory elements coupled to bit line 244. Thetransistors 222 and 224 will select one of these magnetic memoryelements based on the selection of one of the word lines 226 or 228.When a word line is selected, it is biased with the appropriatepotential required to turn on the selected transistors. When one of thetransistors 222 or 224 is selected, the memory element 100 is caused tobe coupled to the circuit 230, at 231, through the transistor 216, whichas a decoder circuit. At the same time the reference memory element 218is selected by the transistor 242 and the word line 220. Thereafter,current flows through the selected transistors, i.e. transistor 222 or224. The current flowing through the reference memory element 218 isalways the same, while current flowing through the selected memoryelements, such as the memory element 100 depends on the state of thatmemory element. That is, if the memory element's state is high, itsassociated resistance (R) is high with respect to the reference memoryelements. Thereafter, less current flows through the selected memoryelements than the reference memory element 218, causing the senseamplifier circuit 230, at 233, to enter a high state with respect tothat of 233. On the other hand, if the selected memory element is at alow state and has low resistance, its current is high with respect tothat of the reference memory element 218 and the voltage at 231 drops.In this manner, the voltage at 231 determines the state of the selectedmemory element.

FIG. 11 shows a non-volatile memory integrated circuit 300 showing anapplication of the memory element 10 of the foregoing embodiments. Thecircuit 300 is shown to include a logic I 302, a logic II 304 andembedded magnetic memory 306. The memory 306 includes an array of thememory elements of the foregoing embodiments of the present invention,such as the memory element 10. The logic I 302 and the logic II 304 areCMOS circuit used for addressing the memory 306.

FIG. 12 shows a process flow chart 310 showing the steps performed inmanufacturing the memory element 10 and corresponding CMOS circuitry. InFIG. 12, at step 312, a CMOS process is performed to form the contactsand requisite CMOS circuits. Next, at step 314, the embedded memory orarray of memory elements 10 is processed and finally, at step 316,metallization and passivation processes are performed, The oxidationstep discussed herein form oxides forming the graded free layers shownand discussed with respect to various embodiments and is performedduring the step 314.

In yet another embodiment of in the graded layer, such as the layer 26,the magnetic anisotropy direction in the layer is varied from in-planeto out-of-plane. This is accomplished by the graded free layer having asubstantially perpendicular component, shown at 424 in FIG. 13. FIG. 13shows the graded free layer 26 having out-of-plane magnetic anisotropy,in accordance with another embodiment of the present invention. Thisfacilitates switching of the free layer by having a more effectiveapplication of the torque from the spins accompanying the conductionelectron thereby leading to a lower switching current. Morespecifically, the spins accompanying the conduction electrons during the“parallelizing” process or the reflected spins in the“anti-parallelizing” direction tend to be substantially parallel to thein-plane direction for the longitudinal orientation. As these spinstravel through the substantially perpendicular component 424 of thegraded free layer 26, which has substantially perpendicular magneticmoments, they impart maximum torque thereby initiating the magneticreversal. This, in turn, begins to pull the magnetizations vectors ofthe spins of the layers that are formed adjacent to the substantiallyperpendicular component, such as the layers 422 and 426, and eventuallyleads to a complete reversal in the free layer. The free layer, due tothe preferred anisotropy from the “elongated” shape and thefield-induced anisotropy along the long-axis, remains in two statesnamely, the parallel or anti-parallel state with the fixed layermagnetization.

In one embodiment of the present invention, the graded free layer has atleast three portions namely, the portion closer to the “barrier” ortunneling layer, marked as layer 422, being an amorphous layer such asCoFeB, then a layer 424 comprised of multi-layer of cobalt (Co),platinum (Pt) and or palladium (Pd). There may be more than fewalternating layer of these elements which are deposited sequentiallytypically using a multi-target sputtering source. In one example athree-layer, Co/Pt multi-layer, is used where the Co layer thickness is0.2 to 0.6 nm and the Pt layer is 0.4 to 1.2 nm thick. In a another,example Pd/Co/Pt multi-layer is used where a the typical stack has 2-5repeated layers and the Pd layer is 0.3 to 1.2 nm thick, Co-layer is 0.2to 0.8 nm thick and the Pt-layer is 0.6 to 1.2 nm thick. Anotherlayer—426 of CoFeB or just CoFe layer may be placed on the top. Layers422, 424 and 426 are collectively referred to as the free-layer. Thelayer 422 is kept primarily amorphous as-deposited to ensure hightunneling-magneto-resistance (TMR) for the memory element afterpost-annealing. It should be pointed out that the TMR depends on therelative magnetic orientations of the magnetic moments on the two sidesof the barrier layer namely, the fixed layer and the layer 422 of thefree layer. A typical thickness of the layer 422 is 0.5 to 3 nm. Thelayer 424 role is to primarily reduce the switching current to ensurelower power for the memory products. The role of the layer 426 is toensure firstly a high degree of polarization of the incoming conductionelectrons from top during the “anti-parallelizing”process whileproviding enough magnetic energy for high enough thermal stability.

FIG. 14 shows a non-volatile magnetic memory element 519, in accordancewith another embodiment of the present invention. In FIG. 14, the memoryelement 519 is shown to include a pinning layer 520 on top of which isshown formed a graded fixed layer 532, on top of which is shown formed asynthetic AF (SAF) coupling layer 534 on top of which is shown formed agraded fixed layer 536, on top of which is shown formed a barrier layer524, on top of which is shown formed a free layer 526, on top of whichis shown formed a cap layer 528. While not shown in FIG. 14, a bottomelectrode is generally formed below the layer 520 and optionally, aseeding layer is formed between the bottom electrode and the layer 520.A top electrode, not shown in FIG. 14, is formed on top of the caplayer. Current is applied from the layer 520 through the top to the caplayer 528. The layers 532 and 536 are each graded fixed layers, whichsandwich the layer 534.

During deposition of the layers 536 and 532, the deposition process isvaried during the deposition of the layer causing grading of the layers536 and 532 in a manner similar to that of building or forming the freelayer, as further discussed above. The graded layers can be achievedduring the deposition by varying the amount of oxygen or other reactivegas component in the sputtering gas, by varying the substrate biasapplied to the wafer, by varying the sputtering power applied to thetarget, by varying the ratio of sputtering powers to two or more targetsduring co-deposition and by bombarding the growing film with ions from aseparate ion source.

The choice of alloys for layers 536 and 532 is one or many ferromagneticelements, such as Co, Fe and Ni, and contains less than 20 atomicpercent of platinum (Pt) and further contains up to 20 atomic percent ofone or more of the following elements: P, B, Cr, Ta, W, Mo, Zr, Hf. Inone embodiment, the layer 536 is a substantially amorphous alloy, suchas a CoFeCrB, where the boron, B, content of the alloy varies between 10to 30 atomic percent in such a way to enhance crystallization of layer536 starting from the barrier layer interface during a subsequentheating process, the layer 536 transforms into a cubic crystal structurehaving (002) plane that is substantially parallel to the barrier layer,which has a cubic crystalline structure being (001), and having theircrystal planes, (001), matched. This type of structure results in thememory element having a very high TMR (tunneling magneto-resistance).

In another embodiment, the layer 532 is a substantially crystallinealloy, such as a CoFeCr, where magnetic moment of the alloy is varied insuch a way as to enhance the exchange-coupling to anti-ferromagneticlayer 520 and enhance the RKKY coupling with layer 536 across the spacerlayer 534. The layer 534 is made of an alloy made of ruthenium (Ru) andelement X which may include one or more of the elements from thefollowing group: chromium (Cr), molybdenum (Mo), tantalum (Ta), rhodium(Rh) or iridium (Ir) which creates RKKY coupling between the adjacentmagnetic layers namely, the layers 532 and 536. The choice of thicknessof the layer 534 results in a parallel or anti-parallel magnetizationacross the magnetic layers 532 and 536. For example, typically athickness of 6 Å to 10 Å results in a strong anti-parallel couplingbetween the two adjacent magnetic layers while a thickness of 12 Å to 18Å results in parallel coupling. The 536 layer can also have more thanone layer. The layer closer to the RuX side is less amorphous but hashigh Ms to get higher RKKY coupling, and to get more polarization of theconduction electrons. The layer closer to the barrier side can be moreamorphous as described above.

Although the present invention has been described in terms of specificembodiments, it is anticipated that alterations and modificationsthereof will no doubt become apparent to those skilled in the art. It istherefore intended that the following claims be interpreted as coveringall such alterations and modification as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A non-volatile magnetic memory elementcomprising: a bottom electrode coupled to the bit line; a seeding layerformed on top of the bottom electrode; a graded free layer formed on topof the seeding layer, the graded free layer including a boron (B) withvaried composition through the graded free layer; a tunnel layer formedon top of the graded free layer; a graded fixed layer formed on top ofthe tunnel layer, the graded fixed layer being of varying compositionsuch that Ms in the composition of the graded fixed layer is greater inareas of the graded fixed layer that are adjacent to the tunnel layerand the Ms decreases in the remaining areas of the graded fixed layerand is the lowest in areas of the graded fixed layer that are farthestfrom the tunnel layer; an anti-ferromagnetic pinning layer formed on topof the graded fixed layer; a cap layer formed on top of theanti-ferromagnetic pinning layer; and a top electrode formed on top ofthe cap layer.
 2. The non-volatile magnetic memory element, as recitedin claim 1, wherein the composition of the B is such that it is ofhigher B content in an area of the graded free layer that is adjacent tothe tunnel layer than the B content in remaining areas of the gradedfree layer with the B content dropping from the area of the graded freelayer that is adjacent to the tunnel layer to a part of the remainingarea of the graded free layer that is farthest from the area of thegraded free layer that is adjacent to the tunnel layer.
 3. Thenon-volatile magnetic memory element, as recited in claim 2, wherein theB content at the area of the graded free layer adjacent to the tunnellayer is 20 atomic percent and 10 atomic percept at the area of thegraded free layer that is farthest from the area of the graded freelayer that is adjacent to the tunnel layer.
 4. The non-volatile magneticmemory element, as recited in claim 1, wherein an area of the gradedfree layer that is adjacent to the tunnel layer has a lower Ms than theremaining areas of the graded free layer wherein the Ms of the gradedfree layer increases from the area of the graded free layer that isadjacent to the tunnel layer to a part of the remaining area of thegraded free layer that is farthest from the area of the graded freelayer that is adjacent to the tunnel layer.
 5. The non-volatile magneticmemory element, as recited in claim 5, wherein the graded fixed layerincludes B with varied composition through the graded fixed layer. 6.The non-volatile magnetic memory element, as recited in claim 5, whereinthe composition of the B in the graded fixed layer is such that it is ofhigher B content in an area of the graded fixed layer that is adjacentto the tunnel layer than the B content in remaining areas of the gradedfixed layer with the B content dropping from the area of the gradedfixed layer that is adjacent to the tunnel layer to a part of theremaining area of the graded fixed layer that is farthest from the areaof the graded fixed layer that is adjacent to the tunnel layer.
 7. Thenon-volatile magnetic memory element, as recited in claim 6, wherein theB content at the area of the graded fixed layer adjacent to the tunnellayer is 20 atomic percent and 10 atomic percept at the area of thegraded fixed layer that is farthest from the area of the graded freelayer that is adjacent to the tunnel layer.
 8. The non-volatile magneticmemory element, as recited in claim 4, wherein an area of the gradedfixed layer that is adjacent to the tunnel layer has a lower Ms than theremaining areas of the graded fixed layer wherein the Ms of the gradedfixed layer increases from the area of the graded fixed layer that isadjacent to the tunnel layer to a part of the remaining area of thegraded fixed layer that is farthest from the area of the graded fixedlayer that is adjacent to the tunnel layer.
 9. The non-volatile magneticmemory element, as recited in claim 1, wherein the tunnel layer is madeof material selected from a group consisting of: titanium dioxide(TiO₂), alumina (Al₂O₃), magnesium oxide (MgO), tantalum oxide (Ta₂O₅),hafnium oxide (HfO₂), zirconium oxide ZrO₂, tantalum nitride (TaN),strontium oxide (SrO), ruthenium oxide (RuO), and zinc oxide (ZnO). 10.The non-volatile magnetic memory element, as recited in claim 9, whereinMgO, includes less than 50 mol % of the compounds from the list ofmaterial of claim
 10. 11. The non-volatile magnetic memory element, asrecited in claim 1, wherein the cap layer serves to insulate the gradedfree layer from the top electrode and in this manner, serves to isolatethe graded free layer from any micro-structural effects of the topelectrode.
 12. The non-volatile magnetic memory element, as recited inclaim 1, wherein the cap layer serves to isolate the graded free layerfrom micro-structural effects associated with the top electrode.
 13. Thenon-volatile magnetic memory element, as recited in claim 1, wherein thecap layer is made of amorphous materials selected from a groupconsisting of: nickel niobium (NiNb), nickel zirconium (NiZr), nickelniobium zirconium (NiNbZr), nickel silicon niobium (NiSiNb), and nickelsilicon zirconium (NiSiZr).
 14. The non-volatile magnetic memoryelement, as recited in claim 1, wherein the cap layer is made of morethan one layer wherein one of the more than one layers is made ofmaterial selected from a group consisting of: copper (Cu), gold (Au) andruthenium (Ru).
 15. The non-volatile magnetic memory element, as recitedin claim 1, wherein the cap layer has a thickness of less than 50nanometers (nm).
 16. The non-volatile magnetic memory element, asrecited in claim 1, wherein the bottom electrode is made of anon-magnetic layer.
 17. The non-volatile magnetic memory element, asrecited in claim 1, wherein the bottom electrode is made of tantalum(Ta).
 18. The non-volatile magnetic memory element, as recited in claim1, wherein the pinning layer is formed to determine the direction ofmagnetization of the fixed layer.
 19. The non-volatile magnetic memoryelement, as recited in claim 1, wherein the fixed layer is made of afirst sub fixed layer formed on top of the pinning layer, a syntheticanti-ferromagnetic coupling layer formed on top of the first sub fixedlayer and a second sub fixed layer formed on top of the syntheticanti-ferromagnetic (AF) coupling layer.
 20. The non-volatile magneticmemory element, as recited in claim 1, wherein the first and second subfixed layers are each alloys made of one or more ferromagnetic elements,such as Co, Fe and Ni, and contains less than 20 atomic percent ofplatinum, Pt and further contains up to 20 atomic percent of one or moreof the following elements: P, B, Cr, Ta, W, Mo, Zr, and Hf.
 21. Thenon-volatile magnetic memory element, as recited in claim 20, whereinthe ferromagnetic elements of the first and second sub fixed layers areselected from a group consisting of: copper (Co), iron (Fe) and nickel(Ni) and includes less than 20 atomic percent of platinum, Pt andfurther includes up to 20 atomic percent of elements made of materialselected from a group consisting of: P, B, Cr, Ta, W, Mo, Zr, and Hf.22. The non-volatile magnetic memory element, as recited in claim 20,wherein the second sub fixed layer is a substantially amorphous alloy.23. The non-volatile magnetic memory element, as recited in claim 20,wherein the second sub fixed layer is made of an alloy copper iron boron(CoFeCrB), where the boron, B, content of the alloy is between 10 to 30atomic percent.
 24. The non-volatile magnetic memory element, as recitedin claim 20, wherein the second sub fixed layer and the graded freelayer are amorphous and transformed into a cubic crystal structurehaving (002) plane parallel to the tunnel layer.
 25. The non-volatilemagnetic memory element, as recited in claim 1, wherein the bottomelectrode has a thickness of less than 100 nanometers (nm).
 26. Thenon-volatile magnetic memory element, as recited in claim 1, whereinpinning layer has a thickness that is less than 20 nanometers (nm). 27.The non-volatile magnetic memory element, as recited in claim 1, whereinthe graded free layer has a magnetic orientation that is changeablerelative to the magnetic orientation of the fixed layer, the graded freelayer being made of nonmagnetic compounds surrounded by magneticregions, the nonmagnetic compounds varying across the thickness of thegraded free layer forming graded contents of oxides or nitrides andshaped substantially like an upside down cone, the graded free layerresponsive to switching current that changes the magnetic orientation ofthe graded free layer, the magnetic orientation of the graded free layerdefining a state stored by the non-volatile magnetic memory element. 28.The non-volatile magnetic memory element, as recited in claim 1, whereinthe nonmagnetic compound of the graded free layer has a reactivityassociated therewith and wherein the graded contents have a thicknessthat is based on the reactivity of the non-magnetic compound.
 29. Thenon-volatile magnetic memory element, as recited in claim 1, wherein thebottom electrode is made using reactive ion etching (RIE) process. 30.The non-volatile magnetic memory element, as recited in claim 1, whereinthe fixed layer includes a first sub fixed layer formed on top of thebarrier layer and on top of the first sub fixed layer is formed asynthetic anti-ferromagnetic (AF) coupling layer on top of which isformed a second sub fixed layer, wherein the AF coupling layerdetermines the direction of magnetization of the fixed layer.
 31. Anon-volatile magnetic memory element, as recited in claim 30 wherein thefirst sub fixed layer is made of a CoFeCrB alloy and wherein the boron,B, content of the CoFeCrB alloy is in the range of 10 to 30 atomicpercent.
 32. The non-volatile magnetic memory element, as recited inclaim 30, wherein the first sub fixed layer and the second sub fixedlayer are each graded having changing composition through the filmthickness.
 33. A memory cell comprising: a bit line; a non-volatilemagnetic memory element including, a bottom electrode coupled to the bitline; a seeding layer formed on top of the bottom electrode; a gradedfree layer formed on top of the seeding layer, the graded free layerincluding a boron (B) with varied composition through the graded freelayer; a tunnel layer formed on top of the graded free layer; a gradedfixed layer formed on top of the tunnel layer, the graded fixed layerbeing of varying composition such that Ms in the composition of thegraded fixed layer is greater in areas of the graded fixed layer thatare adjacent to the tunnel layer and the Ms decreases in the remainingareas of the graded fixed layer and is the lowest in areas of the gradedfixed layer that are farthest from the tunnel layer; ananti-ferromagnetic pinning layer formed on top of the graded fixedlayer; a cap layer formed on top of the anti-ferromagnetic pinninglayer; a top electrode formed on top of the cap layer; an accesstransistor having a source, drain and gate, the drain of the accesstransistor coupled to top electrode; and a word line coupled to the gateof the access transistor, the bit line and the word line operative toselect the memory cell.
 34. The memory cell as recited in claim 33further including a Program/Erase line coupled to the source of theaccess transistor and operative to program or erase the memory cell whenthe memory cell is selected.
 35. The memory cell as recited in claim 33,wherein the composition of the B is such that it is of higher B contentin an area of the graded free layer that is adjacent to the tunnel layerthan the B content in remaining areas of the graded free layer with theB content dropping from the area of the graded free layer that isadjacent to the tunnel layer to a part of the remaining area of thegraded free layer that is farthest from the area of the graded freelayer that is adjacent to the tunnel layer.
 36. The memory cell asrecited in claim 35, wherein the B content at the area of the gradedfree layer adjacent to the tunnel layer is 20 atomic percent and 10atomic percept at the area of the graded free layer that is farthestfrom the area of the graded free layer that is adjacent to the tunnellayer.
 37. The non-volatile magnetic memory element, as recited in claim33, wherein an area of the graded free layer that is adjacent to thetunnel layer has a lower Ms than the remaining areas of the graded freelayer wherein the Ms of the graded free layer increases from the area ofthe graded free layer that is adjacent to the tunnel layer to a part ofthe remaining area of the graded free layer that is farthest from thearea of the graded free layer that is adjacent to the tunnel layer. 38.The non-volatile magnetic memory element, as recited in claim 37,wherein the graded fixed layer includes B with varied compositionthrough the graded fixed layer.
 39. The non-volatile magnetic memoryelement, as recited in claim 38, wherein the composition of the B in thegraded fixed layer is such that it is of higher B content in an area ofthe graded fixed layer that is adjacent to the tunnel layer than the Bcontent in remaining areas of the graded fixed layer with the B contentdropping from the area of the graded fixed layer that is adjacent to thetunnel layer to a part of the remaining area of the graded fixed layerthat is farthest from the area of the graded fixed layer that isadjacent to the tunnel layer.
 40. The non-volatile magnetic memoryelement, as recited in claim 39, wherein the B content at the area ofthe graded fixed layer adjacent to the tunnel layer is 20 atomic percentand 10 atomic percept at the area of the graded fixed layer that isfarthest from the area of the graded free layer that is adjacent to thetunnel layer.
 41. The non-volatile magnetic memory element, as recitedin claim 38, wherein an area of the graded fixed layer that is adjacentto the tunnel layer has a lower Ms than the remaining areas of thegraded fixed layer wherein the Ms of the graded fixed layer increasesfrom the area of the graded fixed layer that is adjacent to the tunnellayer to a part of the remaining area of the graded fixed layer that isfarthest from the area of the graded fixed layer that is adjacent to thetunnel layer.
 42. The non-volatile magnetic memory element, as recitedin claim 33, wherein the tunnel layer is made of material selected froma group consisting of: titanium dioxide (TiO₂), alumina (Al₂O₃),magnesium oxide (MgO), tantalum oxide (Ta₂O₅), hafnium oxide (HfO₂),zirconium oxide ZrO₂, tantalum nitride (TaN), strontium oxide (SrO),ruthenium oxide (RuO), and zinc oxide (ZnO).